A rotary traveling wave oscillator is described in U.S. Pat. No. 6,556,089, which is incorporated by reference into the present application. In that patent, a wave front moves around a closed, differential loop, reversing its polarity in each transit of the loop. The wave front traveling on the loop is established and maintained by a plurality of regeneration elements, such as back to back inverters, distributed about the entire loop. At any point on the differential loop, a differential clock signal is available by making a connection to that point. The frequency of the clock signal is determined by the electrical size of the loop, by which is meant the time it takes to make a lapse around the loop, given the loop's loaded transmission line characteristics.
The rotary clock technology makes it possible to obtain a large number of clock phases from a single physical circuit, creating new architecture possibilities.
For those architectures that need several phases (more than 2) simultaneously, a common solution is a ring oscillator. In that case, the phases order is defined by the circuit order itself. However, ring oscillators have a limited number of phases available, determined mostly by the time delay of the inverter used. Also, the spectral purity and the current/power consumption are known to be critical limitations for the ring oscillator. For applications that need good spectral purity and low power consumption, generation of multiple phases is also possible by injecting multiple oscillators together in such a way that they are operating at the same frequency, but with a well-known phase delay between them. The I/Q (90 degree out of phase) signal generation is a common requirement for wireless systems with modern digital modulation. This solution is practical if a low number of phases is needed.
The rotary clock is ideal for multiple phase generation, the time delay between two phases being mostly defined by the transmission line and the capacitive loading. This time can be significantly lower than the minimum time delay of an inverter for the technology used and the spectral purity of the phases is comparable or better than the standard LC tank solution.